There is a box about a third of the way down the Schedule 1 of the T2 return immediately after the “Net Income (loss) for income tax purposes” that says “Farming income (loss) included in net income (loss) above” The amount you include on this line determines how much flows to Part 1 - Non-capital loss section of the Schedule 4 and how much flows to Part 3 - Farm Loss area of the Schedule 4.
If you are preparing a T2 return for a corporation with Farm Losses, filling in this extra box on Schedule 1 with the proper amount is something you need to remember to do. On a couple of occasions I have forgotten to fill in the figure for farm losses and realized this while I was checking over the Schedule 4.
Perhaps on some future T2 release it might be an idea to include a diagnostic warning on that Schedule 1 field that gets triggered by a negative amount in field 9899 from the Schedule 125. If the warning gets tripped, perhaps a message such as “Does the amount on line E above include any Farm losses?” on that Schedule 1 field.